Modeling the effect of temperature on the yield strength of precipitation strengthening Ni-base superalloys

For describing the temperature-dependent yield strength (TDYS) of precipitation strengthening Ni-base superalloys, a temperature-dependent model of Anti-Phase Boundary (APB) energy was developed in this study firstly. And then combining the proposed temperature-dependent APB energy model with the classical particle shearing theory, two temperature-dependent critical resolved shear stress models were developed for the weak and strong coupled dislocation pairs, respectively. Furthermore, the transition of dislocation motion mode from shearing to by-passing with increasing temperature was described theoretically by defining a temperature-dependent probability function of by-passed precipitate particles. In this way, a TDYS model for precipitation strengthening Ni-base superalloys was developed. The model contains the contributions of the precipitates, the grain boundary, the solid solution and the base metal at different temperatures, and their corresponding variations of the strengthening mechanisms with temperature. Moreover, the TDYS of seven typical precipitation strengthening Ni-base superalloys was predicted, and good agreement is obtained between the predicted results and the experimental data. The contribution of each mechanism to TDYS with increasing temperature was analyzed in this study. It indicates that the transition of dislocation motion mode from shearing to by-passing with increasing temperature will weaken the high-temperature yield strength of precipitation strengthening superalloys. Both grain refinement and solid solution strengthening are effective methods to reduce the probability of transition from particle shearing to by-passing, which can help maintain the high-temperature yield strength of superalloys. Using the proposed TDYS model, the optimal precipitate size to achieve maximum strength at different temperatures was analyzed. As temperature increases, the optimal precipitate size of superalloys decreases. And the optimal precipitate size at the most dangerous service temperature of the alloy can be determined by our model when designing a new superalloy.